This invention concerns an automatic control system of lights in a series circuit illumination system, in particular for lights for airport signalling. It is furthermore possible to utilize the same system for automatic control of road or motorway (motorway crossings or ramps) illumination plants or even for controlling the illumination plant of large industrial areas.
Airport signalling lights or runway lights are not limited to those which illuminate the landing strip to make it well visible to pilots, but also include the taxiway or runway centerline lights which are arranged on the axis of the taxiways, the take-off strip and the routes between the taxiway and the various parking areas. The characteristics, arrangement and functioning of these lights are disciplined by the regulations of the ICAO (International Civil Aviation Organization) which is the international body which controls flight regulations including also those to be respected in the movement of aircraft and vehicles on the ground, in order to guarantee collective safety. The presence of these lights has, in fact, the purpose of giving the pilots and drivers of vehicles circulating in the airport area (such as ambulances, fire engines, vehicles for passenger transport, vehicles for baggage transport, etc) an exact indication of the whereabouts of various airport sectors which can be driven on also in conditions of unfavorable visibility, in particular enabling aircraft pilots to avoid any collisions with the wing tips and to align the aircraft along the axis of the taxiways and the take-off strip.
The use of lights for airport signalling has been proposed in the art as a visual means for disciplining the airport ground traffic in a centralized manner and thus taking it away from the judgement of individual drivers, something which, however, leads to situations of chaos very similar to those encountered in urban motor vehicle traffic. In particular, from the control tower the central lights of the route to be taken are activated progressively in front of the aircraft or motor vehicle to be moved, which is thus enabled to follow. At the intersection between two or more taxiways stop bar lights are positioned horizontally and across the entire width of the individual taxiway. Said stop bar lights if lit up indicate the obligation to stop. In short it concerns a "stop-go" system of guiding the pilot or driver of the motor vehicle, which substitutes and surpasses the function of the classic "follow-me", that is the vehicle which precedes the aircraft at a short distance in front of it to indicate the route which it must follow. The activation of the switching on/off of the central lights present in various runways or taxiways may be carried out manually on the initiative of the personnel of the control tower, or preferably, automatically by means of the relative control system.
In their new function of "intelligent" traffic guiding, the airport signalling lights thus take on a fundamental role for achieving conditions of safety in airport ground traffic and thus are very important in all the above mentioned systems which control their operation automatically.
It is known from WO 90/04242 of a method and a system to supervise and check the field lights in an airport, regulate the intensity of the lights and to receive information regarding the condition of the lights, said method and said system being able to integrate further a system of ground traffic control connecting to proper presence detectors. Said method and said system, as appears clearly in the description of the above-mentioned document and from FIG. 2 thereof, concern almost exclusively the feeding systems of the "parallel" type airport lighting, which is not considered to operate in "series" type systems. It is known for this purpose that the majority of "parallel" type feeding systems for the electrical current of airport lights is realized through DC regulators, series circuits and series transformers for one or more lamps (see diagram 1 of FIG. 1 of WO 90/04242) and without using a "parallel" design (see diagram 2 of FIG. 1 of WO 90/04242). As is evident for a man skilled in the art, the application of the invention according to WO 90/04242 to the already existing "series" type system necessitates inevitably the exclusion of the DC regulators, the substitution of all the distribution cables and the exclusion of all the series field transformers. For what concerns modifications to "parallel" type circuits, they necessarily concern the exclusion of the regulators and the exclusion of the field transformers. From the above, it appears first that the system of WO 90/04242 is reasonably and economically usable only for new systems or, at most, for "parallel" type systems, whose distribution, presently at low level, is destined to diminish in the future.
Further, while the above-mentioned WO 90/04242 provides for the possibility of use for the transmission of data in a dedicated cable, only the use of the same circuitry for feeding through the technology of conveyed waves is described. Thus, there is in the first place the impossibility of switching off the control system of the WO 90/04242 and of the use of the manual system and, hence, in the event of damage or interruption of electric energy in the airport, the communication and the control of the physical position of the airplanes are made impossible.
Various control systems of this type have been proposed, which all have at least one central information processing and command unit, that is a computer, connected to peripheral control units by means of the same network circuit, that is the power circuit which feeds the various lights and regulates the intensity of the current passing through them.
This power supply is in a series circuit, in order that all the lights receive the same intensity of power and may emit the same intensity of brightness. More particularly the feeding of the individual lights occurs by means of the secondary of the same number of insulating transformers, whose primaries are connected in series by means of a suitable power cable. This is so that the burnout of a single lamp does not interrupt the continuity of the circuit and thus the power supply to the other lamps. Suitable devices connected to said cable, "Constant Current Regulators" or CCR, keep the intensity of the current flowing in said cable as constant as possible in the case of fluctuations in the power supply or in the event that some lights do not function and cause a strong unbalance of current to the primary of the transformer concerned and thus to the whole series circuit. So, if on one hand it may seem completely natural and perhaps even economical to exploit the work circuit which feeds the various lights to carry out controls on them, on the other hand it is easy to see that this may lead to various problems which do not make the operation of this type of system completely reliable. It is immediately noticeable, above all, that any physical malfunction in the work circuit prejudices parameters also in the operation of the superimposed control system, without one being able either to discern whether the malfunction originates in the work circuit or in some of the control system equipment. The transmission of the information of the control system by means of the work circuit will not then be as reliable as if a dedicated circuit were used, in that it is subject to all its own interference and those induced by the work circuit. Furthermore the on and off switch for the various lights, for the purpose of regulating airport ground traffic, is brought about by means of the commutators of the work circuit and consequently for sectors and zones, that is for groups of lights and not individual lights. The diagnosis of the working state of individual lights effected by systems known in the art allows the number of malfunctioning lights there are in the system to be established but not identification of which lights these are. This is a considerable problem in that, as it is not known which lights are not functioning, it is necessary to send personnel in a suitable vehicle to all the various runways and taxiways to find them and substitute them, which brings not only a considerable waste of time, but also further aggravation of the airport ground traffic.
A control system has also been proposed which though still exploiting the work circuit, feeds individual lights not by means of insulating transformers but rather by means of individual Light Control Units (LCU), that is electronic devices able to monitor the functioning of the light, to control its switching on or off as well as substitute the CCR in the regulation of the current which passes through the light and thus the intensity of brightness emitted.
Such a system, in theory, would eliminate some of the aforementioned problems in that it would allow the activation of lights individually and not in groups, as well as detecting which lights are broken. In the experimental tests carried out, however, complete inefficiency of the said system in carrying out its planned task of control emerged, the transmission of information on the work circuit being heavily distorted by disturbance. This is perhaps due to the fact that devices able to individualize and distinguish various types of vehicles which move on the runways are incorporated in series into the work circuit, which function on the principle of photocells by means of a "barrier" of microwaves. In any case, when these are functioning, this system would show the abovementioned limits of a control system which is physically superimposed on the work circuit. Furthermore both this and all the other systems known in the art may be installed on the airport runways or taxiways only by interrupting the power supply to the lights, therefore generating a period without service, and only by modifying the work circuit.